Lead-zinc mining has fueled industries for generations, but it leaves a destructive legacy: highly degraded soils. These sites are contaminated with a toxic cocktail of potentially toxic elements (PTEs), primarily lead, zinc, cadmium, and copper, which are left behind in mine tailings. These soils are also characterized by low fertility and often high acidity, which inhibits vegetation and allows these contaminants to spread through wind and water. In a critical review published in Environmental Research Communications, lead author Abdulmannan Rouhani and colleagues analyzed two decades of research to find the most effective strategies for cleaning up these hazardous sites. Their findings show that instead of trying to remove the metals (phytoextraction), the most reliable and sustainable solution is locking them in place using plants, a process called phytostabilization. But to do this, the plants need a powerful assistant.

The review identifies biochar as a critical component in “assisted phytoremediation”. Biochar isn’t just regular charcoal; it’s a highly porous material with a massive surface area and diverse surface functional groups. These properties make it an ideal, cost-effective, and environmentally friendly tool for locking up contaminants. The review synthesizes multiple studies demonstrating biochar’s effectiveness, showing it can be a true game-changer for land reclamation.

The power of biochar lies in its multi-pronged attack on contamination. First, it directly immobilizes the toxic metals through several mechanisms. Many mine soils are acidic, which makes metals more soluble and mobile. Biochar is typically alkaline, so adding it to the soil raises the pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More. This change in chemistry causes metals like lead and cadmium to become less soluble, forcing them to precipitate into solid, stable forms that plants cannot absorb. Second, biochar’s porous structure and high surface area act like a high-capacity filter, adsorbing and complexing metal ions directly onto its surfaces, effectively trapping them. The review highlights field studies in Spain and France where manure-based or mixed biochars reduced the bioavailability of lead by 40-60% and zinc by 25-50%.

By locking away the toxic metals, biochar breaks the cycle of phytotoxicity that normally kills plants. But it doesn’t stop there; it also acts as a powerful soil conditioner. Its porous structure improves soil aeration and water retention, and it increases the soil’s cation exchange capacity (CEC)—its ability to hold onto and provide essential nutrients like nitrogen and phosphorus. Biochar also provides a safe habitat for beneficial soil microbes, such as nitrogen-fixing bacteria, which further rebuild soil fertility. This combination of detoxification and soil improvement creates a healthy environment for plants to thrive. The review cites research on the energy crop Miscanthus x giganteus, where a biochar amendment increased plant height by 20.4% and boosted aboveground biomass by an incredible 115% compared to the untreated toxic soil.

The review concludes that combining tolerant native plants with soil amendments is the most sustainable path forward for these contaminated landscapes. While true “hyperaccumulator” plants that can suck metals out are rare, biochar-assisted phytostabilization offers a practical and effective alternative. By transforming waste into a high-value soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More, biochar tackles two environmental problems at once. It helps establish the healthy, robust vegetation cover necessary to lock toxic metals in place, finally allowing these degraded lands to heal.

Source: Rouhani, A., Newton, R. A., Gusiatin, M. Z., Pidlisnyuk, V., Vila, M. C., & Al Souki, K. S. (2025). PhytoremediationThis is a technique that uses plants to clean up contaminated soil or water. Biochar can enhance phytoremediation by improving soil conditions and promoting plant growth, allowing plants to absorb and break down pollutants more effectively.   More strategies for remediating Potentially Toxic Elements’ polluted soils in lead-zinc mining areas: A critical review. Environmental Research Communications. In press.